My 20 year old Acura’s driverside seat belt hasn’t been retracting easy of late. So I got a bucket with hot water and threw some detergent in it, and let it soak for about a hour. Then I scrubbed with a microfiber towel. I will let it air dry over night. This procedure worked on my 25 year Japanese mini truck in the past. My seat belts are tan, so they show how dirty they are.